This application is based upon and claims the benefit it of priority from the prior Japanese Patent Application No. 2000-286028, filed Sep. 20, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to an optical disk from which an accurate reproduction signal can be obtained when reproduced by a disk drive apparatus by optimally controlling warp created in a disk-shaped recording medium such as an optical disk or a magnetic disk, a method of manufacturing such an optical disk, and an optical disk device which can record data on such an optical disk or reproduce the data from the disk.
A disk drive device which can record data on a disk-shaped recording medium (disk) such as CD-ROM, MO disk or DVD-disk, or can reproduce already recorded data from a disk, is connected to, for example, a personal computer (PC), and thus used so as to supply a system program or software for operating the PC, or for supplying and storing a great amount of data. Alternatively, the disk drive device is connected to, for example, a television or a monitor device, and thus used to reproduce image software or game software.
Since the first music CD was made into practical use, the memory capacities of these disks are increased year by year.
In an optical disk of a DVD-type, a transparent resins such as polycarbonate is used and it is formed by injection molding into a substrate having a surface on which a record pattern is transferred and a flat mirror surface. Then, a reflection film is formed on a data recording surface by, for example, a sputtering method. With this structure, a record pattern is read by making a laser beam incident on the mirror surface.
In this case, in consideration of the productivity, substrates are, in many cases, formed in a cycle of several seconds by injection molding with use of a transparent resin such as polycarbonate.
However, in thin products such as substrates for optic al disks, when the molding in the order of submicrons is performed in a cycle of several seconds by applying such a pressure and heat for transferring a data pattern, it is not inevitable that thus produced substrates have warps due to the remaining stress of the resin.
Nowadays, in order to further increase the density, it will become necessary to increase the pressure applied on a substrate and the temperature of the resin during molding further than those in the current technique as the data patter to be transferred on the substrate becomes finer, and therefore it is expected that the warp of the substrate will become more prominent.
Conventionally, the warp of formed substrates is controlled by adjusting the forming conditions such as the temperature of the metal mold and the pressure for tightening the mold. However, as the data pattern to be transferred on a substrate becomes finer in order to increase the density, the degree of freedom in the forming conditions is lowered. Therefore, it becomes substantially difficult to control the warp by simply adjusting the forming conditions.
As a result, an optical disk which can be obtained by adhering substrates together, is warped, and thus the quality of the reproduction signal is undesirably deteriorated.
In the meantime, when two substrates are adhered together in order to manufacture an optical disk, it is of a general technique that an ultraviolet curing resin is provided between substrates and made into an adhesion layer by a spin coat method. However, in the case where the control of the warp of the formed substrates is not sufficient, and the direction of the radial warp of the substrates is unknown, it becomes difficult to determine the conditions for applying the ultraviolet curing resin when adhering the substrates together. Thus, the uneven distribution of the ultraviolet curing resin applied and run-off of the resin are caused, thereby lowering the yield of the products.
As described above, as the density of the optical disk is increased, the degree of freedom of the forming conditions is lowered. Therefore, it is difficult to control the warp merely by adjusting the forming conditions as in the conventional case. As a result, the warp of the formed substrates, which has becomes even worse, causes an adverse effect on the adhesion of the substrates together and the reproduction of signals.
The present invention has been proposed in consideration of the above-described drawbacks of the conventional technique, and the object thereof is to provide an optical disk having appropriate warp properties for reproducing a signal after application of an ultraviolet curing resin for adhering two substrates and after adhering the substrates together, an optical disks manufacturing method which can produce such optical disks at high yield, and an optical disk apparatus capable of recording data on such an optical disk and reproducing data therefrom.
According to an aspect of the present invention, there is provided an optical disk comprising:
a data recording surface varying a state when irradiated with light;
a first substrate for supporting the data recording surface; and
a second substrate for protecting the data recording surface,
wherein
tilt in a radial direction of the first and second substrates as a whole is 0.5xc2x0 or more and tilt in a tangential direction is 0.10xc2x0 or less.
According to another aspect of the present invention, there is provided a method of manufacturing an optical disk having a data recording surface, comprising the steps of:
forming a first substrate having a data recording surface by injection molding, in which a first metal mold having a predetermined surface curvature in a surface on a cavity side is set to face at a predetermined distance to a second metal mold having a surface curvature in a surface on a cavity side, which corresponds to the surface curvature of the first metal mold in an opposite direction, and a material used to form the first substrate is injected between the first and second metal molds while a stamper holding data to be recorded in advance on the data recording surface is provided for one of the first and second metal molds;
forming a second substrate capable of protecting the data recording surface of the first substrate, by injection molding, in which a first metal mold having a predetermined surface curvature in a surface on a cavity side is set to face at a predetermined distance to a second metal mold having a surface curvature in a surface on a cavity side, which corresponds to the surface curvature of the first metal mold in an opposite direction, and a material used to form the first substrate is injected between the first and second metal molds;
setting a predetermined amount of an ultraviolet curing resin between the substrates; and
adhering the two substrates together while irradiating an ultraviolet ray.
According to still another aspect of the present invention, there is provided a method of manufacturing an optical disk having a data recording surface, comprising the steps of:
forming a first substrate having a data recording surface which is convex with a predetermined curvature, by injection molding, in which a first metal mold having a flat surface on a cavity side is set to face at a predetermined distance to a second metal mold having a flat surface on a cavity side, the metal molds are set to have a predetermined difference in temperature between these metal molds while a stamper holding data to be recorded in advance on the data recording surface is provided for one of the first and second metal molds, and a material used to form the first substrate is injected between the first and second metal molds;
forming a second substrate having a surface corresponding to the data recording surface of the first substrate, which is convex with a predetermined curvature, by injection molding, in which a first metal mold having a flat surface on a cavity side is set to face at a predetermined distance to a second metal mold having a flat surface on a cavity side, the metal molds are set to have a predetermined difference in temperature between these metal molds, and a material used to form the second substrate is injected between the first and second metal molds;
directing these substrates to an inner side such that the convex surfaces face each other, and setting a predetermined amount of an ultraviolet curing resin between the substrates; and
adhering the two substrates together while irradiating an ultraviolet ray.
According to still another aspect of the present invention, there is provided a recording apparatus capable of recording an optical disk having a data recording surface, obtained by adhering two substrates having predetermined curvatures such that convex surfaces of the substrates are adhered surfaces, the apparatus comprising:
a light source for irradiating light;
an optical set for guiding the light from the light source towards an optical disk;
a lens for converging the light transmitted by the optical set at a predetermined position of the data recording surface of the optical disk, and guiding light reflected by the data recording surface to the optical set;
a first light detector for photoelectrically converting the reflection light from the data recording surface, which is returned through the optical set, and outputting a signal corresponding to a difference in distance between the lens and the data recording surface of the optical disk with respect to a focal distance of the lens;
a second light detector for photoelectrically converting the reflection light from the data recording surface, which is returned through the optical set, and outputting a signal corresponding to a difference between a center of a light beam spot formed at a focal point position of the lens and a center of either one of a track and a pit line on the data recording surface of the optical disk;
a third light detector for photoelectrically converting the reflection light from the data recording surface, which is returned through the optical set, and outputting a signal corresponding to a degree of tile of the data recording surface of the optical disk in a radial direction, which is created as the optical disk is rotated;
a first lens movement mechanism for moving the lens in a direction orthogonal to the data recording surface of the optical disk;
a second lens movement mechanism for moving the lens in a direction parallel to the data recording surface of the optical disk such that the center of either one of the track and bit line coincides with the center of the beam spot; and
a radial tilt compensation mechanism for moving the lens in a direction to cancel the tilt in the radial direction detected by the third light detector.
According to still another aspect of the present invention, there is provided a recording apparatus capable of recording an optical disk having a data recording surface, obtained by adhering two substrates having predetermined curvatures such that convex surfaces of the substrates are adhered surfaces, the apparatus comprising:
a light source for irradiating light;
an optical set for guiding the light from the light source towards an optical disk;
a lens for converging the light transmitted by the optical set at a predetermined position of the data recording surface of the optical disk, and guiding light reflected by the data recording surface to the optical set;
a first light detector for photoelectrically converting the reflection light from the data recording surface, which is returned through the optical set, and outputting a signal corresponding to a difference in distance between the lens and the data recording surface of the optical disk with respect to a focal distance of the lens;
a second light detector for photoelectrically converting the reflection light from the data recording surface, which is returned through the optical set, and outputting a signal corresponding to a difference between a center of a light beam spot formed at a focal point position of the lens and a center of either one of a track and a pit line on the data recording surface of the optical disk;
a third light detector for photoelectrically converting the reflection light from the data recording surface, which is returned through the optical set, and outputting a signal corresponding to a degree of tile of the data recording surface of the optical disk in a radial direction, which is created as the optical disk is rotated;
a first lens movement mechanism for moving the lens in a direction orthogonal to the data recording surface of the optical disk;
a second lens movement mechanism for moving the lens in a direction parallel to the data recording surface of the optical disk such that the center of either one of the track and bit line coincides with the center of the beam spot;
a radial tilt compensation mechanism for moving the lens in a direction to cancel the tilt in the radial direction detected by the third light detector; and
a signal reproduction mechanism for photoelectrically converting the reflection light from the data recording surface, which is returned through the optical set, and outputting it as a signal recorded on the data recording surface of the optical disk.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.